Phase-modulated multiplex SPAM pulse program for MQMAS from Fernandez, Malicki, and Mafra




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Malicki and coworkers [Multiplex MQMAS NMR of quadrupolar nuclei, Solid State Nucl. Magn. Reson. 28, 13-21 (2005)] incorporate the multiplex acquisition approach with the SPAM MQMAS sequence. This sequence is a phase-modulated one. There are 4I+1 phases for the first pulse. The second pulse is always an x-pulse. The third pulse has two phases (x and -x). The receiver phase is always x.

In fact, this is a double multiplex acquisition experiment: one on the first pulse with 4I+1 phases and one on the third pulse with two phases.

Multiplex SPAM 3QMAS sequence for I = 3/2

Fig. 1: Phase-modulated multiplex SPAM 3QMAS NMR pulse sequence and antiecho transfer pathway for a spin I = 3/2.

For each t1 value of the MQ evolution period, 2(4I+1) time-domain signals are acquired and stored individually. That is, for each phase k of the first pulse, two time-domain signals are acquired and stored individually: Sk,0(t1, t2) when the third pulse is an x-pulse, and Sk,π(t1, t2) when the third pulse is a -x-pulse.

(A) Coherence transfer pathway 0Q -> pQ -> 0Q -> -1Q

The echo signal Fp,0(t1, t2) associated with this coherence transfer pathway is obtained from (4I + 1) experimental signals Sk,0(t1, t2) and (4I + 1) experimental signals Sk,π(t1, t2):

Echo signal of z-filter CTP from multiplex SPAM

Similarly, the antiecho signal F-p,0(t1, t2) associated with the coherence transfer pathway 0Q -> -pQ -> 0Q -> -1Q is also obtained from these 2(4I + 1) experimental signals:

Antiecho signal of z-filter CTP from multiplex SPAM

The detected signal is Fp,0(t1, t2) + F-p,0(t1, t2).

For a spin I = 3/2, the antiecho signal F-p=3,0(t1, t2) associated with the coherence transfer pathway 0Q -> 3Q -> 0Q -> -1Q is obtained from the 14 experimental signals Sk,0(t1, t2) and Sk,π(t1, t2). Similarly, the echo signal Fp=-3,0(t1, t2) associated with the coherence transfer pathway 0Q -> -3Q -> 0Q -> -1Q is also obtained from these 14 experimental signals.

(B) Coherence transfer pathways 0Q -> pQ -> (-1Q, 1Q) -> -1Q

The echo signal Fp,1(t1, t2) associated with these two coherence transfer pathways is obtained from (4I + 1) experimental signals Sk,0(t1, t2) and (4I + 1) experimental signals Sk,π(t1, t2):

Echo signal of Hahn echo CTP from multiplex SPAM

Similarly, the antiecho signal F-p,1(t1, t2) associated with the two coherence transfer pathways 0Q -> -pQ -> (-1Q, 1Q) -> -1Q is also obtained from these 2(4I + 1) experimental signals:

Antiecho signal in Hahn echo CTP from multiplex SPAM

The detected signal is Fp,1(t1, t2) - F-p,1(t1, t2).

For a spin I = 3/2, the antiecho signal F-p=3,1(t1, t2) associated with the two coherence transfer pathways 0Q -> 3Q -> (-1Q, 1Q) -> -1Q is obtained from the 14 experimental signals Sk,0(t1, t2) and Sk,π(t1, t2). Similarly, the echo signal Fp=-3,1(t1, t2) associated with the two coherence transfer pathways 0Q -> -3Q -> (-1Q, 1Q) -> -1Q is also obtained from these 14 experimental signals.

(C) Code for Avance NMR spectrometers

; mq3qspammultiplex
; phase-modulated SPAM MQMAS sequence
; associated with multiplex acquisition approach, 
; excitation(3Q) - conversion(-1Q, 0Q, 1Q) - tau - (+X)90sel - ACQ(-1Q),
; excitation(3Q) - conversion(-1Q, 0Q, 1Q) - tau - (-X)90sel - ACQ(-1Q),

; 3Q MAS pulse program for nuclei with half-integer quadrupole spin,
; The generated 3D data have to be processed with the AU program:
; MSM (Multiplex SPAM MQ) provided by Fernandez and coworkers,

;parameters:
;PARMODE : 3D
;AQORDER : 3-2-1
;d1 :  recycle delay
;p1 :  excitation pulse at pl11
;p2 :  conversion pulse at pl11
;p3 :  90 degree selective pulse at pl13
;pl1 :  = 120 dB (not used)
;pl11 : power level for excitation and conversion pulse
;pl13 : power level for selective pulse, ca. Pl11 + 30 dB
;d0 :  = 1u or longer
;in0 = 1n10 : 1 rotor period for synchronised experiment
;td3 : 256*n (= TD2 in a 2D z-filter MQMAS experiment)
;td2 : number of rows acquired in the MQ dimension 
;      (= TD1/2 in a 2D z-filter MQMAS experiment)
;td1 : = 2*7 for 3/2-spin, 2*11 for 5/2-spin, and 2*15 for 7/2-spin
;FnMODE : undefined

;Number of rows to acquire in the MQ dimension
define loopcounter nrows
"nrows=td2"

;Number of individual spectra 
define loopcounter np
"np=td1/2"

1 ze                  ; clear memory, new data replace old data,
                      ; switch AD converter to replace mode,
                      ; perform DS before next acquisition,
2 d1                  ; recycle delay,
  10u pl11:f1         ; 10 microsecond delay,
                      ; set high power in f1 channel,
;---------- Sequence MQMAS (3 pulses)
  1.7u:f1 ph1         ; preset the ph1 phase,
  (p1 ph1):f1         ; high-power excitation pulse,
  d0                  ; MQ evolution period,
  1.7u:f1 ph2         ; preset the ph2 phase,
  (p2 ph2):f1         ; high-power conversion pulse,
  10u pl13:f1         ; set low power in f1 channel,
  1.7u:f1 ph3         ; preset the ph3 phase,
  (p3 ph3):f1         ; 90 selective pulse,

;------------ Acquire
  go=2 ph31           ; signal acquisition without phase cycling,
                      ; loop to 2, ns times for averaging,
  10m wr #0 if #0 zd  ; delay for disk I/O, store signal,
                      ; write individuel FIDs,
                      ; increase FID number,
                      ; delete memory data,
                      ; do not perform dummy scans
                      ; with next acquisition,
;------ 2 experiments for SPAM
  10m ip3*2           ; increment the ph3 phase by 180 for SPAM,
  lo to 2 times 2     ; loop to 2 for acquisition

;---np phase experiments for multiplex of the first pulse
  10m rp3             ; reset of the ph3 phase to 0,
  10m ip1             ; increment the ph1 phase for multiplex,
  lo to 2 times np    ; loop to 2 for acquisition of np phases
  10m rp1             ; reset the ph1 phase to 0

;---- Perform time evolution in the MQ dimension
  10m id0             ; increment d0
  lo to 2 times nrows ; loop to 2 for nrows in MQ dimension,
  exit                ; end of the pulse program

; 7 phases for the 3QMAS on 3/2 nucleus (set TD1=7*2=14)
; Comment this line for 5/2 nucleus
ph1=(7) 0             ; excitation pulse phase
; 11 phases for the 3Q and 5QMAS on 5/2 nucleus (set TD1=11*2=22)
; Uncomment the following line for 5/2 nucleus
; ph1=(11) 0

ph2=  0               ; conversion pulse phase
ph3=  0               ; 90 selective pulse
ph31= 0               ; receiver phase

  

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